1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to encoding of an audio signal, and more particularly, to encoding an envelope of a harmonic signal and decoding encoded data.
2. Description of the Related Art
Parametric coding is an example of a method of encoding an audio signal. Assuming that the audio signal to be encoded is formed of only sinusoidal signals and noise signals, the parametric coding method firstly extracts sinusoidal signals from the audio signal to be encoded and encodes remaining signals. In a Harmonic and Individual Lines and Noise (HILN) method which is one of the parametric coding methods, harmonic signals from among the sinusoidal signals are firstly encoded (harmonic coding), then the sinusoidal signals which are non-harmonic signals are encoded (Individual Line Coding), and finally noise signals are encoded.
The harmonic signals are referred to as the sinusoidal signals having frequency (ω, 2ω, 3ω, . . . ), that is, a multiple of frequency ω of a fundamental frequency signal or the sinusoidal signal having a predetermined correction value (ω, 2ω+ε0, 3ω+ε1, . . . ) for a multiple of the fundamental frequency signal. The correction value can be expressed by a specific equation. Since frequency is known when the harmonic signals are encoded, only amplitude and phase need to be coded and thus efficient coding is possible. The efficient coding means that information can be represented by using smaller sized data.
On the other hand, when sinusoidal signals that are not harmonic signals are encoded, the frequency, amplitude, and phase should all be encoded.
When representing the amplitudes of the harmonic signals, a Linear Predictive Coding (LPC) method is used in a HILN coding method. Encoding the amplitudes of the harmonic signals is called encoding an envelope. In envelope coding, an LPC method is used. However, a more efficient method will be suggested in the present invention.